Dry eye syndrome (DES) is an ocular disease caused by the lack of tear flow or excessive tear loss due to evaporation. It is often caused by aging, environmental factors (such as windy weather), fatigue of eyes, as well as nutrition imbalance. Ocular discomfort and irritation are common symptoms of the DES. Wearing contact lens of poor hydrophilic or wettability properties may also result in DES and eye discomfort. Clinical diagnosis of DES and quantifying its degree of severity is of great significance. However, currently there is lack of suitable user friendly precision technique to evaluate the tear film thickness, tear thinning dynamics, and tear breakup thickness.
Several techniques are currently available for direct tear film measurement in a live eye including the fluorescence technique by instilling saline-fluorescence to the tear, noninvasive optical interferometric method using wavelength dependent fringes, and optical coherence tomography (OCT). The fluorescence technique is invasive that may disturb the tear film. The existing OCT technique suffers from poor thickness evaluation accuracy and thus is not promising for tear film evaluation. The wavelength dependent fringe based noninvasive optical interferometric method offers good measurement accuracy but suffers currently from its bulk optics based critical optical alignment and handling.
Optical reflectometry is a maturely developed measurement technique for multilayer optical films. It has been widely used in industry for quantifying multilayer optical film thicknesses for quality inspection and assurance. The multilayer films that can be measured include dielectric, semiconductor, conductor, polymer, and photoresist. The basic requirement for using optical reflectometry technique for multilayer film evaluation is that the film to film boundary is optical quality, there is reasonable refractive index difference between adjacent film layers so that the reflection from the film boundary is visible by the measurement reflectometer, and the film layers are reasonably transparent.
Optical reflectometers have been commercially developed by a number of institutions including Filmetrics Inc., StellarNet Inc., Ocean Optics, and New Span Opto-Technology Inc. However, none of present optical reflectometers have been configured and used for tear film evaluation in an eye as well as water film hydrophilic property evaluation on a contact lens. This invention shows a solution to tear film evaluation in an eye with or without wearing contact lens using the optical reflectometry technique. It is also a solution to water film hydrophilic property evaluation on a contact lens. The fiber coupled optical reflectometer with galvanometer scanner should make the tear film evaluation including tear thickness, tear thinning dynamics, and tear breakup thickness operational friendly.